Within the field of virtual reality two technologies are commonly used. The first determines location and orientation by measuring the strength and phase of the electromagnetic signals induced in a set of receiver coils by a set of transmitter coils. U.S. Pat. Nos. 3,983,474. Sep. 28, 1976 and 4,017,858. Apr. 12, 1977, both by Jack Kuipers teach this art. This technique works only over a very limited range and is subject to interference from metal objects near the sensing volume. It is also difficult to operate more than one electromagnetic localizer system in the same vicinity without interference.
The second method uses the time of transmission of pulses of ultrasonic sound between sets of transmitters and sets of receivers to determine position and orientation. However, the fast response times needed for virtual reality can be obtained only over a short range because of the relatively slow speed of sound. It is also difficult to avoid interference between nearby localization systems and also interference caused by acoustic reflections from hard surfaces. There is little recent patent literature on this technique since it depends on art developed for SONAR and other applications during the last half-century.
Another approach to localization not often used for virtual reality uses light to provide the position and orientation information. This is the approach used in this invention. Several patents deal with optical localization techniques superficially similar to those used in the current invention. These include U.S. Pat. No. 3,846,026. Nov. 5, 1974, by Kenneth H. Waters./Continental Oil Company. In this patent a Rotating Beam Surveying Method and Apparatus is described which measures location via time coded angular variation of a narrow beam of light or other radiation. This is a good approach, but Waters' implementation would be too slow for virtual reality use since a measurement can only be obtained once per revolution of the beam and the practical revolution speed is limited by mechanical considerations.
A similar invention is described in U.S. Pat. No. 4,677,555. Jun. 30, 1987 by Noel Goyet. His Method and Equipment for Automatic Guidance of Earthmoving Machines and Especially Machines for Laying Drainage Elements uses a rotating laser beam to guide earth moving machinery. This invention is basically a variation of Waters' patent. U.S. Pat. No. 4,700,301. Oct. 13, 1987 by Howard L. Dyke, Method of Automatically Steering Agricultural Type Vehicles, is another invention that uses rotating light beams to position vehicles.
Much closer in spirit to this invention, but still lacking the essential elements of dual modulation of the light sources at unique frequencies and of using independent sensors for orientation, is U.S. Pat. No. 5,100,229. Mar. 31, 1992. by Eric Lundberg, Yvan Beliveau, and Timothy Pratt. Their Spatial Positioning System combines a rotating, pulsed laser together with an omnidirectional strobe in a mode similar to an aircraft VOR (VHF, Omnidirectional Ranging) to implement a system for surveying. The important element in their invention is the use of light to transmit both directional information via the rotating beam and timing information via the strobe. This eliminates awkward interconnecting cables required in the previously mentioned inventions, but is still subject to slow response time determined by the beam rotation speed.
Another technology within the prior art is the aircraft VOR navigation system mentioned above. While using radio waves instead of light or near-infrared radiation, the VOR nevertheless uses a combination of a rotating beam and a stationary beam to locate an aircraft relative to the glide path. There is little recent patent literature relevant to VOR navigation, since as with acoustics, this technology has been in use for years.